Cannabinoids can induce psychotic episodes which are time-locked to exposure, outlast the duration of intoxication, and are clinically significant. CIAPP is distinct from 1) the link between adolescent cannabis exposure and later schizophrenia and 2) cannabinoid induced psychotic symptoms that do not persist beyond intoxication. This latter entity, that we refer to as cannabinoid induced acute persistent psychosis (CIAPP), is the focus of this exploratory study. The high rates and earlier onset of cannabis use, the increasing potency of cannabis, the legalization of medical and recreational cannabis use, the increasing availability and use of edible cannabinoid products, the recreational use of highly potent synthetic cannabinoids, and the high rates of emergency department visits related to cannabis, calls for the need to characterize CIAPP. Given the unpredictable occurrence of CIAPP, we propose using a nested, case-control approach that capitalizes on a unique, annually recurring phenomenon: the predictable and ritualistic use of cannabis by large numbers of people during certain festivals and ensuing cases of CIAPP. Every year, millions of people (representative of the general population) in Northern India celebrate certain festivals during which there is widespread use of cannabis. These festivals are followed by a spike in hospitalizations for psychosis at psychiatric facilities. Since these festivls occur at a predetermined time annually, a large number of CIAPP cases and controls can be studied in a planned manner. The proposed exploratory project capitalizes on 1) the predictable occurrence of CIAPP, 2) large numbers of cases (numbers that would be difficult to capture in the US at a single site), 3) a sample that is more representative of the general population than those who participate in laboratory studies, 4) the relative absence of the confounding effects of other drugs, and 5) hospitalization of cases that would permit detailed characterization. Hypotheses: Relative to controls, CIAPP cases will have higher scores on measures of positive and negative symptoms, worse cognitive deficits, and greater deficits in EEG indices of information processing (ASSR [lower ITC and spectral power], P300 [lower amplitude], P50 gating [altered gating ratios] and neural noise [higher LempelZivComplexity]). While most behavioral differences will resolve over time, some cognitive and psychophysiological differences will persist (trait), albeit of lower magnitude. Methods: Cases of CIAPP (n=71) will be compared to controls (n=71) (friends who consumed cannabis but did not develop psychosis). Demographic information, personal and family history of mental illness and drug use, psychosis (PANSS), and cognitive (Cogstate battery) and psychophysiological indices of information processing (P50, P300, ASSR and noise [LZC]) will be assessed 1) at admission (state), 2) around discharge (state and trait), and 3) again, within 6 months post discharge (trait). A long-term goal is to build on this exploratory study a longitudinal study (R01) of CIAPP, since it may portend a recurrent psychotic disorder.